What Are the Semicircular Ear Canals?

The Semicircular Canals

The lateral, superior, and posterior semicircular canals are responsible for the detection of movement and acceleration. This sensory system is located in the inner ear. | Source

Where are the Semicircular Canals Located?

The semicircular canals part of the inner ear, and are located in the bony labyrinth of the mastoid bone. The bony labyrinth contains the cochlea (responsible for hearing), the vestibule (between the cochlea and canals), and the semicircular canals (responsible for balance).

There are three semicircular canals in humans:

The lateral semicircular canal, located on a horizontal axis.

The superior semicircular canal, positioned in a vertical plane that intersects with the posterior canal at a 90° angle.

The posterior semicircular canal, positioned in a vertical plane that intersects with the superior canal at a 90° angle.

The Purpose of Semicircular Canals

The semicircular canals detect movement and acceleration, which are interpreted by the brain to create a sense of balance.

Organs of Balance

What is the Purpose of the Semicircular Canals?

The inner ear is responsible for two senses: hearing and balance. The cochlea is the hearing organ of the ear, and the semicircular canals are the balance organ of the ear. The semicircular canals are filled with a fluid called endolymph. When the head changes position, movement of the endolymph fluid moves past tiny hair cells called cilia in the canals. Tiny, floating particles called otoliths are suspended in the endolympathic fluid, and the movement of these "crystals" enhance the stimulation of the cilia in the canals.

The semicircular canals are oriented in opposite directions on each side of the head. The lateral canals are responsible for detecting motion on a horizontal plane. When a person is spun in a chair, the lateral canals are stimulated to allow the body to know it is moving. The posterior and superior canals detect vertical head motion and rolling sensations.

Vestibular Sensory Illusion in Pilots

A sensory illusion in the vestibular system causes pilots to continually turn a plane in ever-tightening circles, a phenomenon known as the Graveyard Spiral | Source

Aviation Graveyard Spiral

Vestibular Function and Balance

The entire vestibule and semicircular canal system is sometimes referred to as the vestibular system. This system connects to the auditory nerve and sends information about motion and acceleration to the brain. The brain, in turn, uses this information to create a sense of balance.

This system allows humans to stand upright, walk, and correct for changes in elevation. We know when we are spinning, dropping, or falling over. Sometimes, the vestibular system can lead humans astray, as there can be a perception of "leaning" or "turning," even when the human body is headed in a straight direction.

In aviation, there is a phenomenon known as the Graveyard Spiral - the result of a vestibular illusion. Pilots will turn an aircraft and will sense the craft banking into the turn. After a period of time, the inner ear adjusts to this sensation and the "leaning" sensation is lost. When the pilot straightens out the aircraft, it feels like the plane is banking again. If the pilot is not reading the gauges and is flying by sensation alone, he or she will pull back on the yoke and the plane will turn more (which will feel like "going straight" to the pilot). If this cycle continues, the plane will describe tighter and tighter circles, while descending at an ever-increasing rate.

The Graveyard Spiral is often the result of poor weather, as there is no visual indicator of the horizon to aid the pilot's spatial awareness. Pilots must complete "instrument only" training to prevent this phenomenon - when the weather is poor, pilots must fly by the instruments to prevent sensory illusions from occurring.

The Semicircular Canals and Balance

The movement of endolymphatic fluid past hair cells (cilia) is responsible for the sense of balance. | Source

Superior Canal Dehiscence

Rotational Chair Testing

Vestibular Disorders

There are many vestibular disorders that cause dizziness and imbalance in humans. The primary disorders of the balance system in the inner ear are:

Ménière's Disease: in Ménière's Disease, an abnormal amount of endolymphatic fluid accumulates in the inner ear. People with this condition will experience bouts of vertigo, may have tinnitus, vomiting, a rapid heart rate with anxiety, and trembling. The late stage of the disease results in hearing loss, which affects the low frequencies first and may progress to significant levels of hearing loss.

Benign Peroxysmal Positional Vertigo is not a disease or disorder, but will cause a spinning sensation occasionally with head movement. This happens when the otoliths (otoconia) are dislodged and send a disproportionate signal for movement. Symptoms should resolve over time.

Labyrinthitis occurs when there is an infection of the inner ear. This may cause balance problems, hearing loss, and visual disturbances.

Superior Canal Dehiscense is caused by an opening in the bone above the semicircular canals. This condition will create the perception that an object is moving, even when it is stationary. A person with SCD may hear their own voice as abnormally loud. This problem can be surgically corrected if severe, though hearing loss may result from the operation.

Ototoxicity is caused by drugs that are harmful to the inner ear. Some drugs cause hearing loss, some result in vestibular damage, and others affect both the hearing (cochlea) and balance systems. Drugs like Gentimicin and other aminoglycosides are known to affect the hearing and balance system of the inner ear.

Acoustic Neuroma: a tumor that grows on the auditory nerves connected to the cochlea and/or balance system. These tumors are benign (non-malignant), but pose a serious threat to hearing and balance. Surgery may be recommended to remove the tumor, or radiation may be used to try to shrink the tumor.

Perilymph Fistula occurs when there is a tear in the fine membrane between the middle ear and inner ear. This tear allows air pressure to affect the endolymphatic fluid and cause severe vertigo and hearing loss. Bed rest to allow the fistula to heal and surgery are options for treatment.

Secondary Endolymphatic Hydrops has symptoms similar to Ménière's Disease, but is caused by another underlying disorder. Autoimmune disorders or head trauma may cause an excessive amount of endolymphatic fluid to collect in the inner ear.

Mal de Débarquement is the feeling of motion one experiences on dry land after being at sea for an extended period of time. This problem is most likely caused by the brain rather than the inner ear - the brain's balance centers adjust for the continuous motion of being at sea, and continue to misread signals once the motion has stopped for a significant period of time.

Enlarged Vestibular Aqueducts is a congenital disorder caused by a wider-than-normal aqueduct between the vestibular system and the cochlea. This condition is associated with a fluctuating, progressive hearing loss and balance disorders. Children with this condition may walk at a later age, as they must learn to visually compensate for the lack of balance information from the inner ear.

Autoimmune Inner Ear Disorder is caused when the immune system attacks the inner ear. Byproducts of autoimmune diseases like Cogan's Disease can circulate through the body and end up in the endolymphatic fluid of the inner ear. This debris can cause vertigo and balance problems.

Testing the Vestibular System

Test Name

What the Test Measures

How the Test is Performed

Rotational Chair

This test can determine if balance issues are due to vestibular or neurological problems.

The patient is spun in a chair and eye movements are tracked. Other versions of this test include fixation testing (fixating on a dot that moves with the spinning person) and optokinetic testing, where the patient tracks moving stripes with his or her eyes.

Video Electronystagmography

ENG/VNG testing will determine if a balance problem is vestibular in nature.

Eye movements and object tracking are performed first. Then the eyes are observed as the head is moved, to determine if nystagmus is present. Caloric testing is then performed with hot and cold air in the ear, while monitoring for nystagmus.

Computerized Dynamic Posturography

This test determines the source of a balance problem (motor, vestibular, or central)

The patient stands on a plate that moves, and the computer records the patient's efforts to compensate.

These tests are objective, and require no cooperation from the patient. Brainwaves, otoacoustic responses, and muscle action potentials are measured.

Audiometric

Hearing ability.

The patient listens to pure tones at controlled volues in a sound booth.

Dynamic Visual Acuity Testing

Visual acuity when then the head is in motion.

The patient reads a standard eye chart while moving.

Vestibular System Sensory Issues

Development of the Sense of Balance

The vestibular system is the first sensorimotor system to become fully myelinated as a fetus develops. The fetal vestibular system receives stimulation from the mother's movements. Babies are typically born with a fully developed system and begin to hone their sense of balance over time.

Occasionally, children do not have a functional or well-integrated vestibular system. Pediatric balance problems can stem from enlarged vestibular aqueducts or other inner ear anomalies. Some children have sensory integration problems and may seek vestibular stimulation by spinning or swinging frequently.

Children with sensory integration problems in the vestibular pathway will often "zone out" when they are forced to sit still. These children often need to rock, jump, or move to concentrate on tasks. Adults might see these children as "hyper" when these children are simply trying to stimulate their vestibular systems.

Questions & Answers

Questions must be on-topic, written with proper grammar usage, and understandable to a wide audience.

Question:

Does tilting the head back cause activity of the vestibucochlear nerves?

Answer:

Tilting your head back will cause fluid to shift in your semicircular ear canals, which will be relayed via your nervous system to your brain. The fluid in the semicircular canals will allow your brain to determine the relative position of your head and body in space (allowing humans to maintain balance while walking, jumping, and performing other physical activities).

Comments

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AUTHOR

Leah Lefler

6 years agofrom Western New York

Thanks, MickiS! Aviation illusions are really scary - I have a friend who is a pilot and he had to do a lot of training with his vision obstructed. It is amazing how our brains can be tricked when vision is occluded!

MickiS

6 years agofrom San Francisco

This is a fantastic Hub. I had never heard of the graveyard spiral in aviation. Super interesting. My cousin is a small craft pilot, and I've gone up a few times with him, so I can imagine what your videos shows.

AUTHOR

Leah Lefler

6 years agofrom Western New York

There are so many reasons for vertigo/balance issues. I occasionally get benign positional vertigo, teaches12345, but fortunately it isn't very frequent. For me, it feels/looks like everything has turned upside down for a few seconds - it is very disorienting!

Dianna Mendez

6 years ago

This is a great hub and I learned much from your posting the definition and the chart on the tests. A couple of my family members suffer from inner ear imbalance on occasion and I can understand how this happens after reading your article. Thanks for sharing. Voted way up!

AUTHOR

Leah Lefler

6 years agofrom Western New York

Thanks, Om. My son actually has some vestibular issues and his ENT had suggested running some basic testing to determine why he falls occasionally. He has a congenital progressive hearing loss, and we are fairly certain that he has some balance issues when his hearing drops. He'd probably like the rotary chair testing, as he loves to spin!

Om Paramapoonya

6 years ago

Very well-written and nicely formatted! It's so interesting to learn about different types of vestibular system testing. All the videos are also great. I enjoyed this hub from start to finish!

AUTHOR

Leah Lefler

6 years agofrom Western New York

I hope it helps your friend, greatstuff. It could be due to allergies or benign paroxysmal positional vertigo - though he should probably see a doctor to rule out more serious conditions.

Mazlan

6 years agofrom Malaysia

Wow, this is very informative. Will forward this to a friend who suffers from vertigo. He has it on a 'on and off' basis, could be due to allergy as highlighted in your hub. Voted useful and more.

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